Development of space nuclear power and propulsion systems is difficult and costly due to radiation-related health and safety problems during system testing. In order to reduce the health and safety problems, researchers have pursued means for non-nuclear testing of nuclear systems. The non-nuclear testing includes simulation of a nuclear reactor core with electrical heaters. Using a simulated reactor core, various characteristics of the nuclear system that are not directly related to the nuclear operation are tested.
Early stages of conventional nuclear system development utilized resistive electrical heater elements. The resistive electrical heater elements simulate nuclear reactor pins. Conventional resistive electrical heater elements are designed with the same form factor as the simulated nuclear reactor pins, namely a cylindrical structure with an outer metallic clad surrounding a graphite resistive element. The resistive electrical heater elements are bound in a hexagonal packing pattern to simulate the shape of the core structure of the nuclear reactor assembly. Other elements of the reactor design are also incorporated including heat transfer mechanisms, power conversion systems, radiators, and loads. However, the simulated core has thermal loss through the power leads that provide electrical power to the conventional resistance heaters.
Resistance heaters have nuclear pin diameters that are relatively large, greater than 0.5 inches. Power leads of the conventional resistive heaters require relatively large diameter wires to minimize losses in the leads. Since the power leads have electrical resistance, the current passing through the leads produces thermal energy in the leads. In order to minimize the thermal loss, larger diameter wires are used. However, as the lead wire diameter increases, two complications arise. First, the physical placement of the power leads entering the simulated core is problematic. Second, the conduction of thermal energy out of the core via the power leads increases, resulting in a less robust simulation of the nuclear reactor core.
Later reactor designs require smaller pin diameters, such as less than 0.5 inches, and require more pins, such as hundreds, for higher power systems, further exacerbating these problems. These requirements make the use of resistance heaters less attractive.
Inductive heating is commonly used for applications where a metallic structure must be heated. In general, inductive heating uses a coil that carries alternating current (AC) to produce an alternating magnetic field in the test article. The magnetic field induces currents in the test article, which in turn produce thermal energy via resistive losses. However, inductive heating requires high currents in the coil and hence large diameter power leads. Inductive heating also requires that the active heating element be metallic.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a heater with reduced thermal coupling to the outside environment. There is also a need for a heater with a reduced size relative to the power leads. Furthermore, there is a need to generate high thermal energy in a relatively small space to simulate fission reactions for non-nuclear testing in nuclear core development. The above-mentioned shortcomings, disadvantages and problems are addressed by the present radio-frequency driven dielectric heater, which will be understood by reading and studying the following specification.